Posted May. 08, 2005 23:33,
Some experts in the United States suggest that North Korea is preparing for an underground nuclear bomb test. However, indications are not definite enough to confirm the suspicion. This article will examine why North Korea wants to conduct a nuclear test, and how the U.S. and South Korea detect it.
Why Does North Korea Want Nuclear Tests?-
The prominent reason for the alleged nuclear test, if it turns out to be real, will be to check if their atomic bombs work.
North Korea has already conducted high explosive tests, the final stage before a nuclear test, more than 70 times since the end of the 1990s. However, atomic bombs can function properly only when the detonation of high explosives is followed by nuclear reaction. Nuclear fusion should take place in less than one millionth of a second after the explosion. As a minute error can be fatal in the process, a nuclear weapons test is prerequisite for completion of a nuclear weapon.
Experts say North Korea will need several atomic bomb tests. There is another reason why North Korea needs nuclear tests. It probably has plutonium bombs like the ones dropped on Japan during the World War. They even more strongly require tests as they are less advanced bombs than those that use Uranium.
North Korea may also aim to prove its possession of atomic bombs and to be officially accepted as a nuclear power. This may in turn help stabilize its society.
Most Tests Conducted Underground-
Although nuclear weapons can be tested regardless of circumstances: underground, underwater or outer space, underground is most preferred for the sake of secrecy and security.
An underground test leaves no clear evidence. It releases only a seismic wave and a minute amount of radioactive gas, and no sound wave or radioactive substances. For this reason, among 2050 nuclear tests worldwide from 1945 to 1998, 74 percent were conducted underground.
Usual underground tests are done in a hole excavated under the surface. This hinders detection by decreasing the impact of the explosion by ten to 14 percent. The depth of the hole varies according to the power of the bomb tested, from a few hundred meters to one kilometer. As North Korea already owns several underground military bases at more than 80 meters below the ground, intelligence agencies of the U.S. and South Korea say the North will have no problem to prepare a hole for a small-scale atomic explosion.
Detection Capability of the U.S. and South Korean Governments-
If North Korea conducts an underground nuclear test, the seismic wave will be the first sign to reveal it to the U.S. and South Korea intelligence agencies. Seismic waves caused by an underground test are on totally different wavelength from the ones caused by earthquakes, and its epicenters are also different. In two to three minutes, the test will be detected by more than 30 seismological observatories nationwide.
Along the armistice line on the Korean peninsula, seismometers are deployed to detect for the Norths nuclear tests in late 1990s. The system is delicate enough to notice an explosion of a 0.25kt nuclear weapon at a distance of 3800 km, which is much smaller than the ones (20kt) dropped in Japan during the World War.
U.S. spy satellites will also play their part by using their ability to identify 50-centimeter long objects on the earth. It will take detailed photos of the surface before and after the test, and will confirm if a test was conducted. In addition, U.S. forces deployed in Japan will send their spy planes on reconnaissance like RC-135 to the East Sea to sense radioactive gas emitted after the nuclear test.
Therefore, it is impossible for North Korea to conduct a secret underground nuclear test.